[PATCH 3.19 068/101] firmware: dmi_scan: Prevent dmi_num integer overflow

Greg Kroah-Hartman
2015-04-17T13:36:57Z

From: Jean Delvare <jdelvare@suse.de>

commit bfbaafae8519d82d10da6abe75f5766dd5b20475 upstream.

dmi_num is a u16, dmi_len is a u32, so this construct:

dmi_num = dmi_len / 4;

would result in an integer overflow for a DMI table larger than
256 kB. I've never see such a large table so far, but SMBIOS 3.0
makes it possible so maybe we'll see such tables in the future.

So instead of faking a structure count when the entry point does
not provide it, adjust the loop condition in dmi_table() to properly
deal with the case where dmi_num is not set.

This bug was introduced with the initial SMBIOS 3.0 support in commit
fc43026278b2 ("dmi: add support for SMBIOS 3.0 64-bit entry point").

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Matt Fleming <matt.fleming@intel.com>
Cc: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/firmware/dmi_scan.c | 22 +++++++---------------
1 file changed, 7 insertions(+), 15 deletions(-)

--- a/drivers/firmware/dmi_scan.c
+++ b/drivers/firmware/dmi_scan.c
@@ -86,10 +86,13 @@ static void dmi_table(u8 *buf, u32 len,
int i = 0;

/*
- * Stop when we see all the items the table claimed to have
- * OR we run off the end of the table (also happens)
+ * Stop when we have seen all the items the table claimed to have
+ * (SMBIOS < 3.0 only) OR we reach an end-of-table marker OR we run
+ * off the end of the table (should never happen but sometimes does
+ * on bogus implementations.)
*/
- while ((i < num) && (data - buf + sizeof(struct dmi_header)) <= len) {
+ while ((!num || i < num) &&
+ (data - buf + sizeof(struct dmi_header)) <= len) {
const struct dmi_header *dm = (const struct dmi_header *)data;

/*
@@ -529,21 +532,10 @@ static int __init dmi_smbios3_present(co
if (memcmp(buf, "_SM3_", 5) == 0 &&
buf[6] < 32 && dmi_checksum(buf, buf[6])) {
dmi_ver = get_unaligned_be16(buf + 7);
+ dmi_num = 0; /* No longer specified */
dmi_len = get_unaligned_le32(buf + 12);
dmi_base = get_unaligned_le64(buf + 16);

- /*
- * The 64-bit SMBIOS 3.0 entry point no longer has a field
- * containing the number of structures present in the table.
- * Instead, it defines the table size as a maximum size, and
- * relies on the end-of-table structure type (#127) to be used
- * to signal the end of the table.
- * So let's define dmi_num as an upper bound as well: each
- * structure has a 4 byte header, so dmi_len / 4 is an upper
- * bound for the number of structures in the table.
- */
- dmi_num = dmi_len / 4;
-
if (dmi_walk_early(dmi_decode) == 0) {
pr_info("SMBIOS %d.%d present.\n",
dmi_ver >> 8, dmi_ver & 0xFF);